/**
 * Copyright 2007 Jason Horman, Pete Aykroyd
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.functor.expression;

import org.functor.UnaryFunction;

public class Not extends AbstractPredicateExpression implements PredicateExpression {
	private final PredicateExpression predicate;

	public Not(PredicateExpression predicate) {
		this.predicate = predicate;
	}

	public PredicateExpression getPredicate() {
		return predicate;
	}

	public boolean isAlwaysTrue() {
		return getPredicate().isAlwaysFalse();
	}

	public boolean isAlwaysFalse() {
		return getPredicate().isAlwaysTrue();
	}

	public PredicateExpression not() {
		return getPredicate();
	}

	public boolean equals(Object o) {
		if (this == o) return true;
		if (o == null || getClass() != o.getClass()) return false;
		Not that = (Not) o;
		if (!predicate.equals(that.predicate)) return false;
		return true;
	}

	public int computeHashCode() {
		return 37 * predicate.hashCode();
	}

	public static UnaryFunction<Not,PredicateExpression> getPredicate = new UnaryFunction<Not, PredicateExpression>() {
		public PredicateExpression evaluate(Not not) {
			return not.getPredicate();
		}
	};

	public void toString(StringBuilder builder) {
		builder.append("~(").append(predicate).append(")");
	}
}
